I’ve experienced issues with internet calling on my device as well. In my case, it registers as a drop in connection, which returns after a few seconds. This has happened without fail in every internet call (Facebook, Whatsapp) I have made on my phone, which lasted for longer than a few minutes, over WiFi. I have experienced no issues with calls from my computer. I tried following advice on changing my router settings as in My FP3 doesn't like higher 5Ghz Wifi channels, especially channel 116. An internet test for latency provided better results for me when I changed my router to channel 52.